Calculations

Question 1

What is the formula for calculating renal plasma flow (RPF)?

Answer 1

RPF = RBF x (1 - Hematocrit) or RPF = (urine [PAH] x V) / plasma [PAH]

Question 2

How is minute ventilation and alveolar ventilation calculated?

Answer 2

• Minute (L/min) = tidal volume (L) x breaths/min
• Alveolar (L/min) = (tidal volume - dead space volume) x breaths/min

Question 3

What is Winter’s formula?

Answer 3

Expected PaCO₂ = [1.5 x (serum HCO₃^-) + (8 ± 2)]

Question 4

Calculation for half-life (t_1/2) of drug when given volume of distribution (V_d) and clearance rate (CL)?

Answer 4

t_1/2 = (0.7 x V_d) / CL

Question 5

How can you calculated the GFR and the RPF?

Answer 5

• GFR = [U] inulin or creatinine x V / [P] inulin or creatinine
• RPF = [U]_PAH x V / [P]_PAH
• FF = GFR/RPF

*V = urine flow rate (mL/min)

Question 6

Formula for renal blood flow (RBF)?

Answer 6

RBF = RPF / (1 - Hct) or (PAH clearance) / (1 - Hct)

Question 7

How to calculate SV and use this to calculate EF?

Answer 7

• SV = EDV - ESV
• EF = SV / EDV = (EDV - ESV) / (EDV)

Question 8

What is the formula for loading dose and maintenance dose?

Answer 8

• LD = (CP x Vd) / F
• MD = (CP x CL x t) / F

*CP = Css or target steady state [plasma]

* CL = clearance; t = elapsed time btw doses; F = bioavailability